CONNECTOR NEURONS OF THE NERVOUS SYSTEM 133 



the same conclusion, so that this column of cells is now univer- 

 sally considered to give origin to the connector fibres to the 

 motor neurons of the vasodermal muscles forming the sympa- 

 thetic system. To use the nomenclature given in Chapter I 

 for the voluntary system, these cells, with their prolongations, 

 are the primary connector neurons of that system (Fig. 2, .). 

 The cells of Clarke's column on the other hand clearly give origin 

 to the fibres of the direct cerebellar tract, and are to be looked 

 upon as directly concerned with sensory impulses between the 

 periphery and the cerebellum. They with their prolongations 

 belong to the cerebellar relay system of connector neurons, and 

 have no direct connexion with any excitor neurons. 



THE CONNECTOR NEURONS OF THE SACRAL OUTFLOW. 



When we examine the structure of the spinal cord in the region 

 of the second and third sacral nerves, we see again a distinct mass 

 of nerve cells situated laterally on the edge of the grey matter ; 

 these appear to bear the same relation to the connector fibres of 

 the pelvic nerve as those in the lateral horn of the thoracic-lumbar 

 region to the connector fibres of the sympathetic. As yet the 

 experiment has not been made of cutting the pelvic nerve in very 

 young animals and seeing what change occurs in the sacral region 

 of the cord in consequence of such section. 



It seemed to me possible that some of these cells might give 

 origin to fibres, which travelling up the cord for a short distance 

 came out with the lumbar splanchnics, and thus gave origin in 

 the sacral region to certain of the connector fibres of the sympa- 

 thetic system. Dr. Elliott made the experiment of cutting the 

 cord in the region of the last lumbar or first sacral nerve, and 

 allowed time for degeneration of the supposed fibres, but could 

 find no sign of any degeneration in the lumbar splanchnics. 

 Similarly, section of the cervical cord above the thoracic region 

 gave no sign of any degeneration in the thoracic splanchnics. 



Clearly then the cells, which give origin to the connector 

 fibres of the thoracic-lumbar outflow, are strictly confined to the 

 same portion of the spinal cord, and the corresponding cells in 

 the sacral region give origin entirely to the connector fibres in 

 the pelvic nerve. 



